Elementary schoolgirls take part in a rehearsal for a performance in Hanoi on March 11, 2010. The Vietnamese government launched a two-child policy in the early 1960s. The country's population is an estimated 86 million, about two-thirds of whom are under 35 thanks to a post-war poulation explosion. AFP PHOTO/HOANG DINH Nam (Photo credit should read HOANG DINH NAM/AFP/Getty Images)